1. Field of the Invention
The preferred embodiments of present invention relate to, among other things, a lead frame and a resin sealing mold which improve the productivity and quality of a semiconductor device formed by resin sealing, and a method for manufacturing a semiconductor device using the same.
2. Description of the Related Art
The following description sets forth the inventors' knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art. Semiconductor devices have increased in capacity year after year. In accordance with this increase, the number of lead terminals that become various signal lines has tended to increase. In accordance with this tendency, a QFP (Quad Flat Package) type semiconductor device in which lead terminals extend outward from four directions has begun to be used. An example of this is disclosed in, for example, Japanese Unexamined Patent Publication No.
Hereinafter, background examples will be described with reference to the accompanying drawings. In this regard, FIG. 16 is a plan view of a lead frame, FIG. 17 is a perspective view of a mold, and FIG. 18 is a plan view of a lead frame after resin sealing.
A lead frame 1 shown in FIG. 16 can be formed by means of press-working or etching, and herein, six units are provided and semiconductor elements are mounted on the respective units. Each unit has a roughly square stage (island) 2 for mounting a semiconductor element and lead terminals extending in four directions outward around the stage 2. Furthermore, considering a mold, each unit has gates 4 as resin passages at the corners of a sealing region, and holes for air vents when resin-sealing.
A mold 6 adapted to this lead frame 1 includes, as shown in FIG. 17, an upper mold 7 and a lower mold 8. The upper mold 7 and the lower mold 8 have a plurality of cavities 9 which face the stage 2 of the lead frame, pots 10 that are resin injection ports, and runners 11 which connect the cavities 9 and the pots 10 and serve as flow passages for filling the insides of the cavities 9 with a resin.
In this example, one pot 10 is provided for four cavities, and the runners 11 radially extend toward the respective cavities from the pots. The pots 10′ of the upper mold penetrate for injecting a resin from the upper side. Furthermore, cavities are also formed in the upper mold 7 although they are hidden in FIG. 17.
Next, a method for manufacturing a semiconductor device will be described. First, semiconductor elements are mounted on the stages 2 of the lead frame 1 shown in FIG. 16 via a silver paste that is an adhesive agent. The semiconductor element has a plurality of electrodes on the surface (not shown), and is mounted and fixed on the stage. Thereafter, the electrodes and lead terminals 3 are electrically connected by means of wire-bonding.
After thus mounting the semiconductor elements, the lead frame 1 is set between the upper mold 7 and the lower mold 8 shown in FIG. 17. Then, cavities as injection regions are formed by closing the molds.
Next, a resin to be melted is injected from the pots 10′ of the upper mold 7 at a predetermined pressure. The resin flows into the cavities of the upper mold 7 and the lower mold 7 and is filled in the cavities 9 via the runners 11. Then, the semiconductor elements are sealed. Before injecting the resin, air exists inside the cavities 9. However, at the stage of entry of the resin into the cavities, the resin presses the air and the air is released to, for example, air vents made in the upper mold 7. The air vents are formed as gaps that do not allow penetration of the resin.
After the resin is cooled and cured after being filled, the lead frame 1 is released by opening the molds. FIG. 18 shows the lead frame at this point. In this figure, for easy understanding of the resin flows, portions at which the pots and runners had existed when resin-sealing are shown by dashed lines. As clearly understood from FIG. 18, the resin flows in from the pot 10 that is positioned at the center of four sealing regions through the gates 4. Thereby, the semiconductor elements to be mounted on the stage and a part of the lead terminals 3 around the semiconductor elements are covered by the resin to form one package 12.
Subsequently, the connecting portions of the lead terminals 3 are cut, and the separated lead terminals 3 are bent, whereby a QFP type semiconductor device is completed.
As mentioned above, in the background method for manufacturing a semiconductor device, as shown in FIG. 17, air in the cavities 9 is led to the ends of the cavities 9 and then released to the outside from the cavities 9 through the air vents made in the mold. However, when the air is pressed out from the air vents, the resin forms burrs between the lead frame 1 and the upper mold 7 or between the lead frame 1 and the lower mold 8. The thickness of the resin burrs can be as thin as about 30 μm. In some cases, when releasing the package 12 from the mold 6, the resin burrs are not released from the mold together with the package 12 and remain inside the mold. These remaining resin burrs can obstruct the paths for releasing the air inside the cavities during the next time of resin molding. As a result, the air cannot be released to the outside, and the air is compressed and remains inside the cavities 9. This is problematic because voids and unfilled regions are created in the package.
On the other hand, an air vent provided at the mold side has been considered. At a portion corresponding to the air vent, a part 13 of the lead frame exists, which is originally set so as not to be a lead terminal. On this part, resin burrs of about 30 μm are created as in the above-mentioned case. In some cases, the burrs are left on the lead material during mold-release. In such cases, in the next process of lead bending, the resin burrs remaining on the lead frame 13 are crushed and remain on the bending mold. Since the burrs remain on the mold, in the next bending process this bending mold causes defects such as dents on the lead and lead deformation due to the crushed burrs.
In the case of a QFN (Quad Flat Non-leaded Package) type semiconductor device, the back surface can serve as a mounting surface, and the leads exposed to the back surface make electrical connection with a conductive pattern on a mounting substrate. However, in the background manufacturing method, resin burrs are created on at least the lead frame 13 including continuous packages. Therefore, when mounting the above-mentioned semiconductor device on the mounting substrate, mounting failures may occur due to resin burrs created at the package end.
There is a need in the art for improved systems and methods that overcome the above and/or other problems.